1. Field of the Invention
This invention relates to a shell-and-tube type heat exchanger and more particularly to a shell-and-tube type heat exchanger for use in a shell-and-tube type reactor which is used for catalytic gas phase oxidation. It also relates to a method for the production of (meth)acrylic acid characterized by using the shell-and-tube type heat exchanger for a catalytic gas phase oxidation reactor.
2. Description of the Related Art
Such easily polymerizable substances as acrylic acid and methacrylic acid are useful raw materials for the production and are chemical substances which are produced in large quantities in large-scale commercial plants. Generally, (meth)acrylic acid is produced by subjecting a raw material gas such as propylene, propane, isobutylene, acrolein, or mechacrolein to catalytic gas phase oxidation with a molecular oxygen-containing gas in the presence of an oxidizing catalyst. This catalytic gas phase oxidation is an exothermal reaction which generates a large volume of heat. If this generation of heat is left to take its own course, it will eventually result in shortening the service life of the catalyst, entailing the danger of explosion, and causing variation in the selectivity and the yield of the product. In the production of (meth)acrylic acid, therefore, a shell-and-tube type reactor having a plurality of reaction tubes built in the reactor is used with the object of securing a large surface area for exchange of heat, the reaction tubes are packed with a catalyst and the raw material gas is supplied into the reaction tubes with a view to effecting the reaction of catalytic gas phase oxidation, and a heat transfer medium capable of absorbing the heat of reaction is circulated in the reactor for the sake of removing the heat of reaction generated in the reactor.
Concerning the shell-and-tube type heat exchanger for use in the catalytic gas phase oxidation of this nature, for the purpose of practically eliminating the structural restriction imposed by the thermal expansion due to the difference of temperature between the shell side and the tube side in the reactor to bear on the shell side, Japanese Patent No. 2749957 proposes the concept of introducing and discharging a fluid on the shell side by means of an annular conduit concurrently serving as an expansion joint. FIG. 9(a) is a longitudinal cross section of the shell-and-tube type heat exchanger disclosed by the official gazette of the patent identified above and FIG. 9(b) is a cross section taken through FIG. 9(a) along the line A-A′. A shell 901 partitioned with an upper and a lower tube sheet 907 of the shell-and-tube type heat exchanger has the outer periphery thereof covered with an annular conduit 903. The shell side fluid is introduced through an introducing nozzle 913 into an introducing part distributor 915, advanced laterally in one pass through a tube bundle formed of heat-transfer tubes 919 while effecting heat exchange, and then discharged through a distributor for discharging 921, an annular conduit discharging part 911, and a discharging nozzle 917. An upper and a lower bellows 903a, 903b of the annular conduit 903 are disposed as closely approximated to an upper and a lower tube sheet 907 and partition 905 give rise to a flow path for leading the shell side fluid from an introducing part 909 to the discharging part 911. In the part of the interior of the annular conduit 903 to which the shell fluid is not introduced, a support member 935 is disposed so as to support the annular conduit fast in shape. The annular conduit 903 is disposed in a cooler part 950 which is formed above a reacting part 940.
The central part of the shell, however, incurs large pressure drop due to the numerousness of heat-transfer tubes as compared with the part neighboring the partition 905 of the shell. For the purpose of enabling the shell side fluid to flow toward the center of the shell, it is necessary to secure large pressure drop for the part of the distributor closely neighboring the partition and to take a large head to the circulating pump for the shell side fluid. This difficulty in securing the uniformity of the flow of the fluid becomes particularly conspicuous in a heat exchanger having a large inside diameter of shell and has been causing a great hindrance in recent years to the expansion on a large scale of an industrial production process, namely the expansion of equipment. In order that the effect of uniform and high heat transfer may be obtained in the use of the construction under discussion, it is essential that uniform distribution of the flow of the shell side fluid be realized. A concrete method for implementing this realization is not mentioned anywhere exception the statement that the uniform flow can be obtained by adjusting the number of holes in the distributor and the size of the holes.
The partition 905 disposed in the annular conduit 903 are intended to form the flow path for the shell side fluid and, therefore, are required to prevent the shell side fluid from leaking through the sites of their disposition. The annular conduit, however, expands and contracts in itself because it is provided for the purpose of absorbing the thermal expansion of the reactor on the shell side and the tube side. When the shell side fluid leaks through the partitions, it causes a decline in the thermal efficiency.
An object of this invention, therefore, is to provide a shell-and-tube type heat exchanger which is capable of adapting itself for enlargement of equipment, practically eliminating the structural restriction on the shell side, and securing uniform distribution of flow of the shell side fluid.
Another object of this invention is to provide a shell-and-tube type heat exchanger which allows no leakage of the shell side fluid through the partitions disposed on the annular conduit.
Still another object of this invention is to provide a shell-and-tube type heat exchanger which can be advantageously applied to a shell-and-tube type reactor, particularly to a quenching part in a shell-and-tube type reactor requiring provision of the quenching part subsequently to a reaction part as in a method for the production of (meth)acrylic acid and which can secure uniform distribution of the flow of the shell side fluid and further provide a method for the production of (meth)acrylic acid by the use of the shell-and-tube type heat exchanger.